This invention relates generally to the field of sensors for measuring electrical potentials obtained from the surface of the skin, for example, electroencephalogram (EEG), electrocardiogram (ECG), or electromyogram (EMG).
In the past, electroencephalogram (EEG), electrocardiogram (ECG), and electromyogram (EMG) electrodes have needed the assistance of technicians for proper use, and thus have been relegated for use in clinical environments. With the advent of new modem electronic devices, there has developed a need for an electrode sensor that patients may use at home. These new devices allow patients to use new portable medical devices that require electrodes. The electrode needs to be non interfering with the patients hair and needs to be designed so that its use does not require chemicals or gels that can leave a mess. The prior art does not satisfy these requirements.
U.S. Pat. No. 3,508,541, entitled xe2x80x9cElectrode Constructionxe2x80x9d to R. M. Westbrook et al. discloses an electrode device comprising an electrode element formed of an intimately bonded homogeneous mixture of finely divided Ag and AgCl. An elongated resilient skin engaging member, such as a disposable hollow sponge, holds an electrolyte, such as a sodium chloride gel. Additionally, Westbrook et al. discloses an electrode device which is simply applied to the scalp, eliminates motion artifacts, and regardless of such factors as hair tonics, sunburn, hair length/thickness, or perspiration obtains a good, low impedance, contact. The electrode of Westbrook et al. makes no suggestion that a plurality of the elongated resilient skin engaging members would be beneficial in achieving improved contact, and the electrode device configuration is complicated and would be expensive to mass produce.
U.S. Pat. No. 4,195,626 to Schweizer entitled xe2x80x9cDevice for the Production and Application of Body Stimuli Devicesxe2x80x9d, discloses a biofeedback chamber for applying stimuli and for measuring and analyzing a subject""s reaction to control the stimuli. One of the stimulus applicators is a flexible laminar electrode comprising a plurality of reinforced filament bundles, a hollow reservoir and a porous reservoir for holding an electrolyte, and a metal conductor embedded in the porous reservoir. The filament bundles provide capillary action to deliver electrolyte from the porous reservoir to a patient""s skin. Besides the fact that Schweizer""s disclosure is directed to an electrode for a stimulus applicator as opposed to an electrode for measuring biopotentials, Schweizer teaches away from the present invention in that a flexible laminar electrode is formed of a flexible support, two plastic sheets, yet the filament bundles are stiffened with a reinforcement jacket.
U.S. Pat. No. 4,967,038 to Gevins et al. entitled xe2x80x9cDry Electrode Brain wave Recording Systemxe2x80x9d, discloses a semi-rigid helmet containing a plurality of rubber multi-contact electrodes. The electrodes comprise a gold-plated metal pin with one end formed in a rubber base. A plurality of pyramid-shaped rubber fingers, extending from the base, are terminated with conductive round metal tips. Metal flexible wire, attached at a solder point to the pin within the base, extends through the center of each finger to their tips. The flexibility of the multiple fingers allows the electrode to adapt to the local contours of a head. Having redundant, multiple contact points with the scalp improves the connection since it is not dependent on the impedance at a single small point. The rubber multi-contact electrodes of Gevins et al. do not incorporate a mechanism for applying an electrolyte to the scalp in order to improve electrical contact, improve comfort by moistening the skin, and reducing the electrical resistance of the skin. Additionally, Gevens et al. requires electrical conductivity in each of the fingers of their electrode.
U.S. Pat. No. 5,211,184 to Yee et al., entitled xe2x80x9cMethod and Apparatus For Acupuncture Treatmentxe2x80x9d, discloses an electrode assembly for applying an electrical signal to the skin surface. The electrode assembly comprises a hollow body filled with an electrically conductive fluid, a wick-like material for delivering the fluid to a point where one end of the material is in contact with the skin surface, and a metallic cap attached to a second end of the material. Besides the fact that the Yee et al. disclosure is directed to an electrode for applying an electrical signal as opposed to an electrode for measuring biopotentials, there is no suggestion that a plurality of wicks extending from the hollow body would be beneficial in achieving improved contact with the skin surface.
U.S. Pat. No. 6,067,464 to Musha, entitled xe2x80x9cElectrodexe2x80x9d, discloses an electrode for measuring bio-electric waves. The electrode comprises a support member, a piece of absorbent fiber, and a non-corrosive lead. The support member, made of an insulating material such as ceramic, plastic or heat treated synthetic fibers or felt, is disk-shaped with a hollow, concentric cylindrical projection. The absorbent fiber, made of felt, cotton or synthetic fibers, is mounted in the projection on the support with one end extending beyond the edge of the projection. Alternatively, the absorbent fiber may comprise a bundle of carbon powder impregnated hard felt rods with rounded tips. Electrically conductive fluid, such as saline solution, is introduced into the support through an insertion hole formed opposite the projection, and is absorbed by the absorbent fiber. The electrically conductive fluid may also comprise various skin conditioners, counterirritant materials, anti-inflammatory agents, and astringents. A lead, made of a bundle of carbon fibers, makes contact with the absorbent fiber through the wall of the projection. Musha teaches away from the present invention by incorporating an insertion hole for introducing electrically conductive fluid into the electrode before and during use as opposed to including a reservoir for holding sufficient electrically conductive fluid for the life of the electrode. Additionally, there is no suggestion that a support comprising a plurality of projections, each with an absorbent fiber, would be beneficial in achieving improved contact with the skin surface.
These conventional sensor configurations described above each fail to disclose at least a single significant attribute of the present invention. What is needed is an electrode which may be used on open skin, or skin covered with hair, does not require the use of external gels or waxes to obtain adequate electrical conduction to the skin surface, may be comfortably worn for long periods of time, and may be properly applied to an individual""s scalp without the assistance of a technician.
One advantage of the invention is that it provides a sensor which can be used on open skin, or skin covered with hair and does not require the use of external gels or waxes to obtain adequate electrical conduction to the skin surface.
Another advantage of the present invention is that it provides a sensor which can be comfortably worn for long periods of time.
Yet, another advantage of the present invention is that it provides a sensor which can be applied by the individual wearing the sensor. Hence, no technician is required.
To achieve the foregoing and other advantages, in accordance with all of the invention as embodied and broadly described herein, a sensor for biopotential measurements comprising at least one elastomeric bristle having a base and a tip with a channel running therebetween and a porous wick extending through the channel, the tip contacting a skin surface; a reservoir containing an electrically conductive material is formed at the base of said elastomeric bristle; and an electrode for detecting electrical potential. The porous wick transports the electrically conductive material from the reservoir to the elastomeric bristle tip in order to conduct an electrical signal obtained from the skin surface, moisten the skin surface, and reduce the electrical resistance of the skin surface.
In yet a further aspect of the invention, a sensor for biopotential measurements wherein the reservoir is formed of at least one of: a porous material; and a hollow vessel capable of holding an electrically conductive liquid. The Theological properties of the electrically conductive liquid may be optimized for predictable flow through the porous wick onto the skin surface.
In yet a further aspect of the invention, a sensor for biopotential measurements comprising: a plurality of physically linked and electrically isolated elastomeric bristles, each having a base and a tip with a channel running therebetween, the tip contacting a skin surface; and an electrode for detecting electrical potential. The channel may be filled with a hydrogel material which is formulated to have high electrical conductivity in order to conduct an electrical signal obtained from the skin surface, moisten the skin surface, and reduce the electrical resistance of the skin surface.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.